Conventionally, coating with a hard film of TiN, TiCN, TiAlN, etc. has been performed for the purpose of enhancing the wear resistance of a jig using a cemented carbide, a cermet, a high-speed tool steel, an alloy tool steel, etc. as the substrate.
In recent years, accompanying an increase in the hardness of a work material and a speedup of the cutting rate, a hard film having more enhanced wear resistance is required. Therefore, it is also attempted to apply, as a hard film, a nitride or an oxide each containing at least any one element of Ti, Cr and Al. This hard film has high hardness and excellent oxidation resistance and therefore, is used as a wear-resistant film by being made to coat a surface of a cutting tool, a forming tool or a machine component.
However, such a hard film exhibits a high friction coefficient with various work materials and suffers from the defect of readily causing seizure (so-called “galling”) in a sliding environment. This defect is caused similarly in an environment using a wet lubricant.
A technique for achieving enhancement of the wear resistance by focusing attention not on the material of the hard film but on the surface profile thereof has been proposed. As regards such a technique, for example, Patent Document 1 has proposed a technique of smoothing the hard film surface to an arithmetic mean roughness Ra of 0.05 μm or less so as to decrease a surface defect, improve the galling resistance and oxidation resistance, and thereby enhance the wear resistance. Owing to this technique, it is expected also in the cutting tool field to enhance the wear resistance similarly by the surface profile. However, the effect of improving the wear resistance only by controlling the arithmetic mean roughness Ra to 0.05 μm or less is insufficient in fact.
In particular, for enabling high-speed cutting of, as a work material, a high-hardness member such as cast iron, a cutting tool having more improved wear resistance than ever before must be realized.